The fact that the new superconductors, of so-called high critical temperature, are made of ceramic constitutes a great handicap because they are much more difficult to use in practice than metal superconductors of low critical temperature. The problem arises particularly when making flexible conductors such as multifilament wires and cables.
However, one family among these new compounds has a ductility which, although it does not approach that of metals, allows the production of wires by drawing or of tapes by lamination, using the method known as "powder in metal tube"; it comprises compounds (Bi.sub.2-x Pb.sub.x).sub.2 Sr.sub.2 Ca.sub.n Cu.sub.n+1 O.sub.2n+6 (where 0.ltoreq.n.ltoreq.2), the "ductility" of which is a major advantage.
In contrast, compound Y.sub.1 Ba.sub.2 Cu.sub.3 O.sub.7 hereinafter known as Y123, although having significant advantages over the other compounds, has the usual characteristics of hardness and brittleness associated with ceramics; this has been deplored by many authors in the following publications:
______________________________________ (1) R. FLUCKIGER: VI International Workshop on Critical Currents 8/11 July 91 Cambridge U.K. (2) T. NISHIO: Journal of Materials Science Vol 24 (1989) p. 3228-34 (3) D. F. LEE; K. SALAMA: Physica C 181 (1991) 81-87 (4) S. JIN et al: Materials Science and Engineering B7 (1991) 243-260. ______________________________________